Pistol. The advantage with a pistol is that it's small, less cumbersome, can hold a weaponlight and still be operated with one hand, has higher magazine capacity and you can shoot faster. Recoil is also less for staying on target. If you use quality ammunition like HSTs or another tactical bonded JHP designed to not clog, you have a lower propensity for over-penetration. Shotguns do devastating damage to the body, but they're very cumbersome weapons IMO.